1. Field of the Invention
This invention relates to an apparatus for measuring the distance between an object and the apparatus, and more particularly to an apparatus for detecting the focus of the imaging lens of a camera or the like with respect to an object.
2. Description of the Prior Art
Apparatus for measuring the light from an object passed through an imaging lens such as the phototaking lens of a camera and detecting the amount of deviation of the image plane between the predetermined imaging plane of the lens, for example, the film surface of the camera, and the actual imaging plane of the object are disclosed in U.S. Pat. Nos. 4,185,191 and 4,264,810. In these conventional apparatus, lights emitted from two areas in the exit pupil of the imaging lens which are symmetric with respect to the optical axis are caused to enter a pair of photoelectric conversion element arrays disposed closely adjacent to the predetermined imaging plane of the imaging lens and the outputs of the two arrays are compared, whereby the focus of the imaging lens with respect to the object is detected. From the comparison of the outputs of the two arrays, a critical value can be obtained during in-focus. To achieve strict focus detection, the pair of photoelectric conversion element arrays are required to be disposed with high positional accuracy so that the light-receiving surfaces thereof lie on the predetermined imaging plane of the imaging lens or a plane conjugate therewith. Particularly, in a single lens reflex camera wherein a phototaking lens is utilized as the imaging lens for focus detection, the space in which the photoelectric conversion element arrays are allowed to be disposed is very much limited. Usually, the array for receiving the light reflected by a movable reflecting mirror is disposed in the viewfinder optical system while the array for receiving the light passed through the light-transmitting portion of the reflecting mirror is disposed at the bottom of the mirror box. In any case, the space in which a detector device including the arrays is disposed must be chosen so as not to interfere with the viewfinder light beam or the phototaking light beam.